In a secondary fiber papermaking mill, paper, such as tissue, is made from secondary fiber furnishes, such as recycled office paper, newspaper, and magazines, obtained in municipal curbside paper collections and business paper waste collection, for example. Papermaking fibers are extracted from the waste paper sources and supplied to a conventional papermaking machine. Since the source of the papermaking fibers is waste paper, other materials not useful for papermaking are also usually present. These contrary materials, and the water in which the source materials are carried, must be processed efficiently and handled and disposed of in an environmentally responsible manner.
The use of secondary fiber furnishes continues to increase in the manufacture of pulp and paper. The economic feasibility of using such secondary furnishes depends on the fraction of useful fiber that can be extracted from the total furnish. The size of this useful fiber fraction, known as the yield, depends in large part on the type of waste paper that makes up the furnish. Secondary furnishes, as mentioned, contain substantial amounts of materials not useful for making paper, called contrary materials, for example, fiber fines, staples, paper clips, inks, clays, and the like. While the theoretical yield of a furnish can be determined with precision, perfect recovery of the theoretical yield has yet to be achieved because of technological deficiencies in the recovery processes in current use, or other difficulties.
Conventional processes, as a result of such deficiencies, reject useful fiber that is then lost to disposal. The actual yield of such conventional processes may be increased by the recovery of this fiber.